1. Field of the Invention
The present invention relates to a process for producing 1,1,3,3-tetramethylguanidine which is useful as intermediates or raw materials for manufacturing medicines and chemical products, and also relates to a process for producing dimethylcyanamide which is important as the intermediate for 1,1,3,3-tetramethylguanidine.
2. Description of the Prior Art
It is known that dimethylcyanamide can be produced by reacting cyanogen chloride with dimethylamine in an organic solvent which is immiscible with water (British Patent No. 1267318), by reacting cyanogen halide with dimethylamine in an aqueous solvent (Japanese Patent Application Laid-Open No. 55-133352), or by treating sodium or potassium cyanide and dimethylamine with chlorine in an aqueous solvent (Japanese Patent Application Laid-Open No. 61-280463). The dimethylcyanamide thus obtained is used as an intermediate for the synthesis of 1,1,3,3-tetramethylguanidine. 1,1,3,3-Tetramethylguanidine has been produced by reacting dimethylcyanamide with dimethylamine hydrochloride in a water-immiscible organic solvent at high temperature under pressure (British Patent No. 1267318), or by reacting dimethylcyanamide with dimethylamine and dimethylamine hydrochloride in an aqueous solvent (Japanese Patent Application Laid-Open Nos. 61-280463 and No. 55-133352).
A method of producing 1,1,3,3-tetramethylguanidine from dimethylcyanamide in a water-immiscible organic solvent generally involves several problems. The method requires a complicated reaction apparatus because the reaction is carried out at high temperatures under pressure. The reaction conditions are corrosive to the reaction apparatus. Further, the method does not produce 1,1,3,3-tetramethylguanidine in satisfactory yields. In consequence, 1,1,3,3-tetramethylguanidine is produced from dimethylcyanamide preferably in an aqueous solvent as taught by Japanese Patent Application Laid-Open No. 55-133352.
Therefore, the method of British Patent No. 1267318, in which dimethylcyanamide is produced in a water-immiscible organic solvent, is unsuitable because solid matters such as dimethylamine hydrochloride are precipitated during the reaction and the water-immiscible organic solvent must be changed to an aqueous solvent in the subsequent synthesis of 1,1,3,3-tetramethylguanidine in an aqueous solvent.
A method of mixing an aqueous solution of cyanogen chloride with an aqueous solution of dimethylamine is also unsatisfactory in the yields as described in Comparative Example 1. Japanese Patent Application Laid-Open No. 55-133352 discloses in Example 3 that the final yield of 1,1,3,3-tetramethylguanidine amounts to 85.1 mol % by feeding a cyanogen chloride gas into an aqueous solution of dimethylamine. The low yield of 1,1,3,3-tetramethylguanidine of the proposed method would be attributable mainly to a low yield of dimethylcyanamide intermediate.
The method of Japanese Patent Application Laid-Open No. 61-280463 is favorable for producing 1,1,3,3-tetramethylguanidine in an aqueous solvent because dimethylcyanamide is obtained as an aqueous solution. However, the reaction procedures are complicated because chlorine as an oxidant should be blown into a solution containing a reductive organic compound. Further, as described below, the results of applicants' replication of the proposed reaction procedures showed that the reaction involved possible danger of causing fire.
Therefore, an object of the present invention is to provide a simple process for producing dimethylcyanamide safely in high yields. Another object of the present invention is to provide a simple process for producing 1,1,3,3-tetramethylguanidine safely in high yields via dimethylcyanamide.